U.S. Pat. No. 4,425,805 to Ogura et al. discloses a respiration flow meter including a tube through which a patient blows air. A pair of recesses on the inner wall of the tube or conduit are diagonally aligned with respect to the longitudinal axial centerline of the respiration tube. A pair of ultrasonic transducers are mounted on the inner wall of the recesses. Electronic circuitry determines the velocity of the air flow through the tube by measuring the time differential between the transmission and reception of ultrasonic waves from one transducer to the other when the air in the tube is at rest and when air in the tube is placed in motion due to exhaling or inhaling of air by the patient. The velocity of the air is calculated based upon this time differential.
European patent publication No. 496,156 A2 (herein EP '156). EP '156 discloses an ultrasonic air flow measuring device having an ultrasonic transmitter spaced apart from an ultrasonic receiver, both of which are mounted on a pair of legs spaced about 0.1 meters apart. These legs are inserted into an air flow passage. By monitoring the time differential between the ultrasonic pulse in moving air as compared with the ultrasonic pulse in still air, the air flow measuring device is capable of measuring the velocity of air. The reference or base number for "still air" is determined either by sampling the external air temperature using a thermistor probe and determining the reference or base number using a known relationship between the speed of sound in still air at the measured temperature or by actually measuring the time difference between a transmitted and the received ultrasonic signal in still air. The flow measuring device in EP '156 measures air flow only between the legs retaining the transmitter and the detector.
PCT publication WO 91/09281, published Jun. 27, 1991 discloses an ultrasonic flow meter having a W-shaped ultrasound path inside a measurement tube. The tube also has a stepped elevation/depression on the internal wall of the tube at the site of reflection. The acoustic wave is generally V-shaped.
Canadian published patent disclosure No. 2,071,876 discloses an ultrasonic flow meter. The published Canadian patent application corresponds to published patent document PCT WO 91/09281. The Canadian '876 patent disclosure illustrates an ultrasonic flow meter which includes a tube through which a medium flows. The ultrasonic acoustic path lies within the interior of the tube. The transducer and receiver are fitted in a known manner to the side wall of the tube. It is preferred that the acoustic path or acoustic beam pass diagonally through the longitudinal axial centerline of the flow tube. This is an oblique injection of the ultrasonic waves. The obliquely injected ultrasonic waves are reflected in three successive reflections at the inner wall of the tube generating a W-shaped path between the transmitter and the receiver.
U.S. Pat. No. 4,493,216 to Hassler discloses a method and apparatus for conducting flow measurements on flow ting media utilizing an ultrasonic doppler method. The Hassler patent disclosure indicates that with the ultrasonic doppler method, it is known that flow measurements can be utilized to obtain flow velocity, flow cross-section data and volume flow. The Hassler ultrasonic flow detector includes a support carrying a small, centrally located ultrasonic transducer and larger ultrasonic transducer which surrounds the smaller, centrally located transducer. The support and the transducer heads are placed on the skin of a patient in order to detect blood flow through the arterial and venous systems of the patient.
U.S. Pat. No. 4,438,652 to Saito discloses an ultrasonic doppler flow meter wherein an ultrasonic wave is emitted into a fluid and a reflected ultrasonic wave is sensed due to a reflector in the fluid, such as a slurry contained in the fluid. In greater detail, the transmitted ultrasonic wave is subjected to a frequency modulation corresponding to the velocity of the reflected wave from the reflector or slurry in the fluid.
Canadian published patent application No. 2,079,213 discloses a gas or liquid ultrasonic flow meter. The ultrasonic flow meter includes a transmitter and a receiver wherein the receiver is in an optical path which is concentrically located on a special surface. A focused reflection of the ultrasonic wave is provided for in the ultrasonic acoustic radiation path.
U.S. Pat. No. 4,611,496 to Komachi discloses an ultrasonic flow meter using continuously generated ultrasonic waves. The Komachi patent disclosure states that in a conventional flow meter, the ultrasonic pulse beam is transmitted into the fluid so that the flow rate is obtained from the propagation time of the pulse in the fluid, that is, the flow rate is measured from the time difference between the transmitted and received ultrasonic pulses. In a continuous wave ultrasonic device, the ultrasonic beam is transmitted into the fluid for transmission directly to the ultrasonic receiver provided at another position in the fluid. The flow rate of the fluid is obtained from the phase difference or another quantity and depends upon the flow rate. Particularly, the Komachi ultrasonic flow meter generates a continuous ultrasonic wave which is not in the form of an ultrasonic beam but is rather establishes a standing wave in the cross-section of the tube and a propagating wave in the axial direction of the tube.
U.S. Pat. No. 4,922,750 to Magori utilizes an ultrasound phase different calculation method for measuring high flow rates. The Magori ultrasonic device utilizes a method for detecting the phase difference and is particularly related to measuring the flow of intake air into motor vehicles. Two ultrasonic transducers and two ultrasonic receivers are utilized such that the sonic waves from each transmitter cross the path of the flow media in an X-shaped pattern. Particularly, one receiver is down stream its respective transmitter and the other receiver is upstream its respective transmitter.
Canadian patent disclosure No. 1,297,186 discusses a procedure for analyzing the air content of a liquid or a suspension, for example, a pulp slurry. The disclosure states that measurements of attenuated ultrasonic waves reveal characteristics of a liquid or suspension and particularly pulp slurry. This method determines the attenuation of an ultrasound pulse when the ultrasonic wave is exponentially attenuated as a function of its path length. The Canadian '186 disclosure to measures a characteristic of the slurry based upon the attenuated intensity of the ultrasonic wave and the scattered intensity of that ultrasonic wave.
PCT published patent document WO 91/09280 discloses an ultrasonic gas/fluid flow meter. The ultrasonic fluid flow meter utilizes two transducers generating a W-shaped acoustic wave in the flow tube.
PCT published patent document WO 91/06830 discloses a variable area obstruction gas flow meter. This flow meter includes a variable area obstruction which is mounted in a conduit. The variable area obstruction comprises elastic membranes consisting of first, second and third leaves which extend into the flow stream.
U.S. Pat. No. 4,519,260 to Fu et al. discloses the use of ultrasonic transducers and various applications thereof. Particularly, the Fu patent disclosure illustrates two ultrasonic transducers used to measure blood volume flow and imaging subcutaneous parts of a patient.
U.S. Pat. No. 4,823,612 to Ichino discloses a socket structure for mounting ultrasonic gas flow measuring devices. The socket structure mounts ultrasonic gas flow measuring devices in a gas flow pipe. Ichino states that it is well known in the art to propagate ultrasonic waves through a gas flowing through a pipe in order to measure the velocity and particularly the flow velocity of the gas. The transmitter and receiver are obliquely disposed with respect to the longitudinal axial centerline of the pipe which contains the flowing gas.